I would rotate when the bag runs out, so maybe every 2 months depending on the bag size.
I think it's better to do one food at a time, then rotate it out when you're done the bag instead of mixing them all together. This way, if the dog has a reaction to the food, it'll be easier to pinpoint which food. Also, rotating when the bag runs out gives the dog variety every few months.
Mind you, I've only rotated once for Bitsy since I haven't had her for too long. But I do this for my two cats and it's been working wonderfully. |